Fluorotetraferriphlogopite

Chemical formula: KMg<sub>3</sub>Fe<sup>3+</sup>Si<sub>3</sub>O<sub>10</sub>F<sub>2</sub>

Fluorotetraferriphlogopite is a rare mica group mineral, an iron- and fluorine-rich analogue of phlogopite, forming small, tabular crystals.

## Characteristics Fluorotetraferriphlogopite is a mineral belonging to the mica group, specifically to the biotite series. It is a fluorine-rich and iron-rich (Fe³⁺) analogue of phlogopite. It forms very small, thin, tabular or platy crystals, often with a hexagonal outline, reaching up to 0.3 mm in size. It usually occurs as fine, disseminated flakes or small aggregates. ## Physical Properties This mineral is characterized by perfect cleavage in one direction, which is typical for micas. It has a vitreous to pearly luster on cleavage surfaces. It is a relatively soft mineral, with a hardness estimated at approximately 2.5 on the Mohs scale. Its density is about 3.12 g/cm³. ## Colors and Varieties Fluorotetraferriphlogopite has a characteristic reddish-brown color. No distinct color varieties or commercial varieties have been identified. ## History and Name The mineral's name refers to its chemical composition – indicating the presence of fluorine (Fluoro-), the dominance of trivalent iron (-tetraferri-), and its structural similarity to phlogopite (-phlogopite). It was officially recognized by the International Mineralogical Association (IMA) in 2010 under the number IMA2010-042. It was described based on material from fumaroles of Mount Vesuvius in Italy.

Properties

Mohs hardness
2.5
Luster
Vitreous to Pearly
Streak
Light brown
Density
3.12
Cleavage
Perfect on {001}
Fracture
Micaceous
Transparency
Translucent to opaque in thicker fragments
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of this mineral is possible almost exclusively using advanced analytical methods, such as Raman spectroscopy, electron microprobe (EDS/WDS), or X-ray diffraction (XRD). Visually, it is practically indistinguishable from other fine-grained, brown micas (e.g., biotite, phlogopite). ## Distinguishing from Similar Minerals It is distinguished from other mica group minerals (biotite, phlogopite, lepidolite) by its unique chemical composition, particularly its high fluorine and trivalent iron content. Visual differentiation within this group without analysis is unreliable. ## Crystal Forms It forms very small, thin, hexagonal plates and flakes, rarely exceeding 0.3 mm in diameter. It occurs as individual crystals or small, loose aggregates on the surface of the host rock.

Geological environment

## Genesis Fluorotetraferriphlogopite is a mineral of volcanic origin, crystallizing in a high-temperature exhalation (fumarole) environment. It forms by sublimation from volcanic gases at temperatures of approximately 500-600°C. ## Mineral Associations In its type locality (Vesuvius), it co-occurs with hematite, cryolithionite, and phlogopite. ## Localities This is an extremely rare mineral. Besides its type locality, the fumaroles of Mount Vesuvius in Campania, Italy, its occurrence has been confirmed in the Tolbachik volcanic complex in Kamchatka, Russia.

Rarity

Extremely rare

For collectors

## Quality Criteria Due to the microscopic nature of the crystals, the collector's value of a specimen primarily depends on the confirmation of its identity by a reliable laboratory. Highly valued are rich clusters of well-formed, though still microscopic, crystals on a natural rock matrix, originating from one of the two known localities. Precise documentation and a label with an analytically confirmed mineral name are crucial.

Care and storage

## Cleaning Specimens should be cleaned only with extreme care, using compressed air to remove dust. Due to the extreme delicacy and small size of the crystals, any contact with water, brushes, or other mechanical tools is discouraged. ## What to Avoid Avoid contact with all chemicals, including acids and bases. The mineral is very soft and brittle, susceptible to scratches and mechanical damage. Protect it from ultrasound and sudden temperature changes. ## Storage Microscopic specimens should be stored in specialized micromount boxes, protecting them from dust, moisture, and physical damage. Avoid exposure to vibrations.

Sources

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